Anti-Raveling Knitted Fabrics and Method of Their Making

ABSTRACT

An anti-raveling knitted fabrics and method of their fabrication, which contains a bond between yarn segments at a percentage of the places where yarn segments cross over each other in forming the stitches of the fabric. The bond is formed in the presetting stage where the fabric is subject to a heating-cooling process under a set of empirically determined parameters that control the bond formation and the bonding percentage in the fabric. The bond can effectively stop raveling when there is a fracture and break of yarns in the fabric. This method can be applied to both weft-knitted and warp-knitted fabrics.

FIELD OF THE INVENTION

The present invention relates to a method for preventing raveling of knitted fabrics and to the knitted fabrics produced with this method. Particularly, it relates to a method that produces bonding at crossovers of the yarns forming the stitches in a knitted fabric, thereby preventing raveling even if one of the yarns is broken within the knitted fabric.

BACKGROUND OF THE INVENTION

The principle of knitting is to manufacture fabrics by making loops with yarns. There are mainly two types of knitting: weft knitting and warp knitting.

In weft knitting, the yarn is provided horizontally and make loop in horizontal direction to manufacture fabrics. It uses one continuous yarn to form courses, or rows of loops, across a fabric. One the other hand, in warp knitting, yarns are provided vertically and make loop in vertical direction to manufacture fabrics. It requires one yarn for every stitch in the row or course. With a warp knitting machine, a plurality of yarns is fed from warp beams to a row of needles extending across the width of the machine. The needles, each looping its own thread, produce parallel rows of loops simultaneously that are interlocked in a zigzag pattern.

While warp knitted fabrics are less prone to edge-curling and raveling, known shortcomings of weft knitted fabrics, some warp-knitted fabrics with certain stitch structures also have the raveling problem. Such fabrics may not show any raveling problems during the knitting process and finishing treatment, but the resulting fabrics, when subject to moderate tearing forces, such as being washed in a washing machine, would disintegrated into pieces, much like being cut by scissors as shown in FIG. 8. The following three warp-knitted fabrics are examples that have the aforementioned raveling problem. Of course, such raveling problem is not limited to these examples, and may exist in other warp knitted fabrics.

Fabric 1. Lapping Number Threading (Lapping Diagram in FIG. 1) GB1: 1-0/1-2// Full-Set GB2: 1-0/1-2// Full-Set

Fabric 2 Lapping Number Threading (Lapping Diagram in FIG. 2) GB1: 0-1/1-0// Full-Set GB2: 2-2/0-0// Full-Set

Fabric 3 Lapping Number Threading (Lapping Diagram in FIG. 3) GB1: 0-1/2-1// Full-Set GB2: 0-1/2-1// Full-Set

Due to the stitch structure of the above fabrics, raveling/tearing can occur in the direction opposite to the knitting direction. Raveling refers to separation of yarns or loops due to fracture of a yarn or release of the interlocked loops. When it happens, the loops will ravel from the fracture point along the longitudinal direction, sometimes in the reverse of the knitting direction.

FIG. 4 is a structural graph of the knitted fabric of FIG. 3. It is obvious that when one of the yarns (two yarns are shown: black and gray) is fractured, it can be drawn off thread in the reverse of the knitting direction, resulting in a break of the fabric as shown in FIG. 8.

FIG. 5( a) and (b) are the front and back structural graphs of a weft knitted fabric, respectively. FIG. 6( a) and (b) show two possible raveling situations when one of the yarns fractures, which can be drawn off thread along the latitudinal direction.

DESCRIPTION OF THE INVENTION

One of the object of the present invention is to provide a method that prevents raveling of both weft-knitted and warp-knitted fabrics, by creating bounds between yarn segments at the locations where they are crossing over each other in forming stitches in the fabric. According to the present invention, the fabric must include at least two different yarns. One of the yarns must have a lower melting point than the other yarn(s) and, after being heated to a certain temperature and then cooled down, can create bond between contacting yarn segments where they cross over each other in forming stitches in the fabric. The melting point of this bond forming yarn should be in the range between 150 and 220° C. A preferred bond forming yarn is made of polyamide (i.e., a polyamide yarn). When used with a polyamide yarn, the other yarn(s) must thus have a higher melting point. Other than the melting point requirement, the other yarn(s) can be of any material deemed suitable to a particular situation by people with ordinary skill in the art. For example, a nylon yarn can be used with a polyamide yarn in practicing the invention.

In general, the manufacturing process of knitted fabrics comprises the following stages: warping, knitting, oil-removing, presetting, dyeing and finishing. According to the present invention, the above described bond formed between the yarns may be created at a stage after the knitting step. The preferred stage to create the bond is during the presetting stage.

During the presetting stage, to form the bond between yarns at crossover points, the newly knitted fabric (weft-knitted or warp-knitted), undergone the oil-removing treatment, is subject to heating treatment, for example, with a high-temperature air flow, so that the molecules on the surface of the lower melting point yarn (a polyamide yarn, for example) are in a proper melting state. Under this state, the contact of the yarns at the crossover location will form a degree of melt-integration, which creates the bond between the yarns when the fabric is subject to a quick cooling treatment. The bond formed between the yarns at the crossover point can effectively stop raveling in case one of the yarns in the fabric for whatever reason breaks, as shown in FIG. 7 and FIG. 8 as examples for warped-knitted fabrics and weft-knitted fabrics, respectively.

To form a suitable bond among the yarns in the knitted fabric during the presetting treatment, various parameters, such as temperature and treating duration, must be carefully selected. For example, if the temperature is too high, the yarn may become brittle or broken by too high a degree of melting. If the temperature is too low, there may not be enough melting on the surface of the yarn to form a bond at the crossover point. The parameters, however, may be selected by empirical determination, which can be performed by people of ordinary skill in the art.

In general, the parameters should be chosen so as to produce the bonding at 5%-20% of the yarn crossover points in the fabric. The preferred bonding rate is 10%. The bonding rate determination is within ordinary skill of the art. The bonding rate may affect the physical properties and hand feels of the resulting knitted fabrics and, again, people of ordinary skill in the art may adjust the bonding rate to suite a particular need.

Another object of the present invention is to provide a method of overcoming the defect that may occur during the knitting process. Such defect may create holes in the fabric which are visible to human eyes. When such holes are detected, they can be temporarily closed by sewing, and then be fixed after undergoing the bond-forming process of the present invention.

The oil-removing process is important to subsequent treatments of the fabric. The more thorough the oil-removing is, the better for forming the bond as above described because the bonding formation depends on the melting state of the yarn surfaces.

Not all yarns can serve as a bond-forming yarn that is necessary for practice the present invention. Even among the yarns of the same material, some yarns are suitable to be used as the bond-forming yarn called for by the present invention, while others may be totally unsuitable. However, the yarn selection can be easily conducted by empirical determination. For example, applicant easily determined that among eight different polyamide yarns tested only one was suitable for forming bond according to the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the stitch structure of a warp-knitted fabric.

FIG. 2 shows the stitch structure of a second warp-knitted fabric.

FIG. 3 shows the stitch structure of a third warp-knitted fabric.

FIG. 4 shows loop formation with the stitch structure shown in FIG. 3.

FIG. 5 is diagrams showing the front view (a) and back view (b) of a weft-knitted fabric.

FIG. 6 shows two ways of raveling upon breaking of a yarn of in a conventional weft-knitted fabric.

FIG. 7 shows bonding at yarn crossover location and prevention of raveling when a yarn in a warp-knitted fabric breaks according to the present invention.

FIG. 8 shows bonding at yarn crossover location and prevention of raveling when a yarn in a weft-knitted fabric breaks according to the present invention.

FIG. 9 is a photograph of a warp-knitted fabric (without applying the method of the present invention) being disintegrated into strips after it was washed in a washing machine.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS EXAMPLE 1

In this example, a warp-knitted fabric was fabricated. Except for adding the step of ensuring bonding formation in the presetting stage, the fabrication process was conventional, comprising the stages of warping, knitting, oil-removing, presetting, dyeing and finishing treatment. The fabric was made with yarns, a polyamide yarn sold under the trademark INVISTA and a nylon yarn which has a higher melting temperature than the polyamide, knitted with two guide bars. The lapping number was 0-1/2-1// for both yarns (see FIG. 3).

FIG. 7 shows a photograph of the fabric taken after the treatment that removed the nylon yarn to show more clearly the bond formation by the polyamide yarn in the fabrics. At the crossover points marked by A and B, it can be seen that a bond was formed at each point between segments of the polyamide yarn. Near point B, the yarn was broken but raveling could not continue in the reverse of the knitting direction, due to the bond formed at point B.

During the presetting stage, by empirical determination (i.e., a try-and-error process), the following parameters of heating treatment of the fabric was selected to ensure proper formation of the bond between crossed over polyamide yarn segments of the stitches in the fabric:

The heat treatment was conducted in a hot air chamber which has 8 sections with the overall length of 24 meters, with the entrance opening and exit opening at each end of the chamber, respectively. Each section is 3 meters long and the temperature in each section can be set independently. The fabric moved through the hot air chamber passing through each of the 8 sections from the entrance opening to the exit opening. In each section of the hot air chamber, there is a top air outlet blowing hot air (upper air flow) downward towards the passing-though fabric and a bottom air outlet blowing hot air (lower air flow) upward towards the passing-though fabric. As the upper air flow and lower air flow are blowing in exactly opposite directions, their forces on the passing-through fabric are cancelled each other.

A satisfactory bond-forming result was obtained through the hot air treatment conducted in the above-described hot air chamber under the following settings:

Air Chamber Section No 1 2 3 4 5 6 7 8 Temperature 180 185 185 185 185 185 185 185 (° C.) Upper Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Lower Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Fabric Width 150 160 160 160 160 160 160 160 (cm)

-   Fabric moving speed: 18 meter/minute -   Fabric density at entrance: 52CPC (course per cm) -   Fabric density at exit: 54CPC -   Fabric breadth at exit: 156 cm -   Fabric mass density: 160 g/m² -   Presetting temperature: 185° C. -   Duration within the hot air chamber: 80 second

EXAMPLE 2

A satisfactory bond-forming result was obtained for the same fabric as described in example 1 except the hot air treatment was conducted in the above-described hot air chamber under the following settings:

Air Chamber Section No 1 2 3 4 5 6 7 8 Temperature 180 190 190 190 190 190 190 190 (° C.) Upper Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Lower Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Fabric Width 150 160 160 160 160 160 160 160 (cm)

-   Fabric moving speed: 14 meter/minute -   Fabric density at entrance: 52CPC (course per cm) -   Fabric density at exit: 54CPC -   Fabric breadth at exit: 156 cm -   Fabric mass density: 160 g/m² -   Presetting temperature: 190° C. -   Duration within the hot air chamber: 103 second

EXAMPLE 3

A satisfactory bond-forming result was obtained for the same fabric as described in example 1 except the hot air treatment was conducted in the above-described hot air chamber under the following settings:

Air Chamber Section No 1 2 3 4 5 6 7 8 Temperature 180 193 193 193 193 193 193 193 (° C.) Upper Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Lower Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Fabric Width 150 160 160 160 160 160 160 160 (cm)

-   Fabric moving speed: 20 meter/minute -   Fabric density at entrance: 52CPC (course per cm) -   Fabric density at exit: 54CPC -   Fabric breadth at exit: 156 cm -   Fabric mass density: 160 g/m² -   Presetting temperature: 193° C. -   Duration within the hot air chamber: 72 second

EXAMPLE 4

A satisfactory bond-forming result was obtained for the same fabric as described in example 1 except the hot air treatment was conducted in the above-described hot air chamber under the following settings:

Air Chamber Section No 1 2 3 4 5 6 7 8 Temperature 190 196 196 196 196 196 196 196 (° C.) Upper Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Lower Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Fabric Width 150 160 160 160 160 160 160 160 (cm)

-   Fabric moving speed: 20 meter/minute -   Fabric density at entrance: 52CPC (course per cm) -   Fabric density at exit: 54CPC -   Fabric breadth at exit: 156 cm -   Fabric mass density: 160 g/m² -   Presetting temperature: 196° C. -   Duration within the hot air chamber: 72 second

EXAMPLE 5

A satisfactory bond-forming result was obtained for the same fabric as described in example 1 except the hot air treatment was conducted in the above-described hot air chamber under the following settings:

Air Chamber Section No 1 2 3 4 5 6 7 8 Temperature 180 200 200 200 200 200 200 200 (° C.) Upper Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Lower Air 90% 90% 90% 90% 90% 90% 90% 90% Flow Fabric Width 150 160 160 160 160 160 160 160 (cm)

-   Fabric moving speed: 24 meter/minute -   Fabric density at entrance: 52CPC (course per cm) -   Fabric density at exit: 54CPC -   Fabric breadth at exit: 156 cm -   Fabric mass density: 160 g/m² -   Presetting temperature: 200° C. -   Duration within the hot air chamber: 60 second

As used in this patent, the term “bond” means adhesion between segments of a yarn, which is formed in a heating-cooling process where the contacting surfaces of the yarn segments were first melt to a certain degree by heat and then the co-melted surfaces are cooled to form an adhesion or bonding therebetween.

While there have been described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes, in the form and details of the embodiments illustrated, may be made by those skilled in the art without departing from the spirit of the invention. The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims. 

1. A knitted fabric, comprising a first yarn and a second yarn forming a plurality of stitches, wherein said first yarn has a melting point lower than said second yarn; segments of said first yarn cross over each other in forming said stitches and result in a plurality of crossover points; and at a percentage of said crossover points there is a bond formed between said segments of said first yarn.
 2. The knitted fabric according to claim 1, said first yarn is a polyamide yarn.
 3. The knitted fabric according to claim 2, wherein said second yarn is a nylon yarn.
 4. The knitted fabric according to claim 2, wherein said percentage of said crossover points is between 5% to 15%.
 5. The knitted fabric according to claim 2, wherein said percentage of said crossover points is about 10%.
 6. The knitted fabric according co claim 2, wherein said knitted fabric is a weft-knitted fabric.
 7. The knitted fabric according co claim 2, wherein said knitted fabric is a warp-knitted fabric.
 8. The knitted fabric according to claim 7, wherein said knitted fabric is knitted using a lapping number of 1-0/1-2// for both said first yarn and said second yarn.
 9. The knitted fabric according to claim 7, wherein said knitted fabric is knitted using a lapping number of 1-0/2-1// for both said first yarn and said second yarn.
 10. The knitted fabric according to claim 7, wherein said knitted fabric is knitted using a lapping number of 0-1/1-0// for said first yarn and a lapping number of 2-2/0-0// for said second yarn.
 11. The knitted fabric according to claim 7, wherein said knitted fabric is knitted using a lapping number of 2-2/0-0// for said first yarn and a lapping number of 0-1/1-0// for said second yarn.
 12. A method of producing a knitted fabric of claim 1, comprising a step of empirically determine parameters for a presetting stage so that a suitable percentage of bonding is formed in said fabric.
 13. The method according to claim 12, wherein said presetting stage is conducted in an air chamber having one or more sections and said parameters comprises the temperature, speed in each of said sections. 